In U.S. Pat. No. 4,536,658, issued Aug. 20, 1985, entitled "Hybrid Schottky Infrared Focal Plane Array" C. E. Ludington discloses a hybrid assembly that includes a two dimensional focal plane array (FPA) of Schottky-barrier internal emission photodiodes. The array detects wavelengths longer than 1.0 micron; that is, radiation associated with the infrared (IR) spectrum. In an article entitled "A Wide Spectral Band Photodetector with PtSi/p-Si Schottky-Barrier" by M. Kimata et al., International Journal of Infrared and Millimeter Waves, vol. 6, no. 10, pages 1031-1041 (1985) there is disclosed a monolithic, Schottky-barrier FPA. The array includes a capability to sense, in addition to IR radiation, radiation having wavelengths less than 1.0 micron, including wavelengths associated with the visible spectrum. This additional capability is achieved by frontside illuminating the array, but at the expense of compromised IR performance. IR response is compromised for the reason that a resonant cavity structure is not provided.
In an article entitled "PtSi Schottky-Barrier Focal Plane Arrays for Multispectral Imaging in Ultraviolet, Visible, and Infrared Spectral Bands", by B. Tsaur et al., IEEE Electron Device Letters, vol. 11, no. 4, pages 162-164 (April 1990) there is also described a frontside illuminated array. This array also eliminates a frontside optical cavity structure. The article refers to a thinned Si substrate that is said could improve collection efficiency for carriers generated in the Si and which is said to have been employed in the fabrication of high-performance backside illuminated charge-coupled-device (CCD) imager arrays. The disadvantages of thinning the substrate include a lower fabrication yield and a greater susceptibility to surface recombination effects.
One disadvantage to such frontside illuminated devices of the prior art is that a fill-factor of the array is less than optimum. That is, these prior art Schottky-barrier arrays require that incidant radiation pass through frontside metalization and also the silicide layer. As a result, some significant portion of the radiation that impinges on the frontside of the array is lost to reflection or is otherwise not available for generating detectable charge carriers.
It is an object of this invention to provide a backside illuminated Schottky-barrier photodetector that is responsive to a wide spectral range including both visible and infrared radiation and that achieves a fill-factor approaching 100 percent.
It is a further object of the invention to provide a backside illuminated Schottky-barrier photodetector that provides a high resistivity thinned silicon detector material for detecting wavelengths shorter than one micron and a silicide layer for detecting wavelengths longer than one micron, without sacrificing the beneficial effects provided by a frontside resonant cavity structure.